The present invention relates to semiconductor devices, and more specifically, to a semiconductor device including a physical unclonable function (PUF).
Device variability is typically caused by process variation(s), and it is much more substantial in smaller devices. Such variability is significant in proper circuit operation, and process improvements are made in order to tighten the device variability. Recently, device variability is being sought and applied to enforce security in information technology. As the security of internet-related networks, circuits, and applications becomes ever more stringent, it has become desirable to protect the information shared among semiconductor device communication.
One approach for preventing the unauthorized cloning of semiconductor devices is the use of Physical Unclonable Function (PUF) to encode a physical semiconductor device with a random set of numerical bits. A PUF generates a set of numerical bits, for example, 128 bits to form a matrix “A” A calculation of Y=A*X is performed during operation of the PUF, where “A” is a matrix having elements generated from the PUF, “X” is an input vector called a “challenge,” and “Y” is the output vector called the “response.” The matrix “A” and the input vector should only be known to the chip owner such that only the owner may know if the response is correct.
The PUF is typically embodied in the physical semiconductor device, and introduced a random variation in the threshold voltage (Vt) between a pair of transistor structures which is easy to evaluate but hard to predict. Each pair of transistor structures outputs either a “0” bit or a “1” bit. The bits generated from the PUF in one chip must be fixed and constant over time. In addition, the correlation among the bits generated from different PUF chips must be random. A semiconductor device including a PUF must be easy to fabricate but practically impossible to duplicate (i.e., is unclonable), even given the manufacturing process that fabricates the device. Conventional methods of fabricating a semiconductor device including a PUF typically add one or more PUF fabrication processes into the standard semiconductor device process flow. The added PUF fabrication processes, however, can increase the overall cost to fabricate the semiconductor device.